This invention relates a novel spun yarn having a unique configuration and a process for the manufacture thereof. More particularly, this invention relates to a novel spun yarn which improve efficiency in the manufacture of knitted and woven fabrics and impart useful properties to the knitted and woven fabrics and an effective process for the manufacture thereof.
In general, conventional yarns to be used for the manufacture of knitted and woven fabrics are classified into spun yarns and filament yarns.
Although conventional spun yarns have good bulkiness and are accordingly soft and warm featured, they are limited in uniformity of yarn evenness. Especially, when fine yarn is manufactured from fibers of coarse denier, the uniformity of yarn evenness remarkably becomes worse. Thus, knitted and woven fabrics made of conventional spun yarns are lacking in the uniformity of the surface and, especially, it is difficult to manufacture knitted and woven faberics having high gauge.
On the other hand, conventional filament yarns have good uniformity and even the finer yarns can be manufactured. However, they are lacking in bulkiness and, therefore, knitted and woven fabrics made of them having uniform surface though, are of cold and slim featured. Much research effort has been directed and many methods have been proposed to remove these defects of the conventional yarns.
Conventional methods of obtaining spun yarns are clasified into card system and tow system, and the tow system includes perlock system, tarbo stapler system, converter system and direct spinning system. In the card system that is the mechanism of making spun yarn to open and rearrange staple fibers from fiber mass in which staple fibers are arranged randomly, the obtained spun yarn is limited in evenness and it is said that the limit of evenness of spun yarn corresponds to that in random slivers.
In other words, when the average number of fibers in cross section of spun yarn is N, the rate of yarn evenness in randon slivers, CV.sub.o, is the following. EQU CV.sub.o = 100/.sqroot.N
and the rate of yarn evenness in the spun yarn obtained by the card system is always beyond the value of the above equation.
The rate of yarn evenness means a coefficient of variation in unevenness of finess of spun yarn, and the lower the value, the better the evenness of yarn. In the tow system, the method of obtaining staple fibers from tow is either to tear off the tow or to cut the tow by a knife.
In the latter case, the end portions of staple fibers obtained are centralized at a specific position along the length of sliver, and therefore a useful yarn can not be obtained. In order to disperse the cut end portions of staple fibers, doubling and drafting are repeated, so that the uniformity of finess of the obtained spun yarn is almost equal to the uniformity in spun yarn obtained by the card system. In the former case or the method of obtaining sliver by tearing off, the uniformity of thickness of the sliver is deemed as follows. The number of filaments, which compose a supplying tow, is represented as n, and it is supporsed that all of the filaments are of the same finess and elongation of each filament at tearing off is perfectly recovered. When the tow is torn off at drafting of D times to obtain sliver, the average number of fibers in cross section of two becomes n/D. Further, supposing that the cutting of filaments randomly takes place, probability p of existing of one of the filaments, in the optional cross section of sliver becomes 1/D and probability q of non-existing of it becomes (1-p). EQU p = 1/D EQU q = 1 - p
The number of fibers in cross section of sliver is obtained by adding them n times, and as a result of binomial distribution, probability P(r) of the number of fiber in cross section being r becomes the following. EQU P(r) = nCrP.sup.r q.sup.n-r
As dispersion of data at binomial distribution is n.multidot.p.multidot.q and the average value is n.multidot.p, CV% of data becomes the following. EQU (.sqroot.n.multidot.p.multidot.q/n.multidot.p) .times. 100 = .sqroot.(q/n.multidot.p) .times. 100 = .sqroot.(D-1/n) .times. 100 .sup.(%)
In other words, when a tow, which is composed of n pieces of filaments, is teared off at drafting of D times to obtain sliver, supposing that the cutting of filaments randomly takes place, the number of fibers in cross section, CV%, of becomes EQU .sqroot.(D-1/n) .times. 100%.
On the other hand, CV% of the above mentioned random sliver is (100/.sqroot.N)%. N is the average number of fibers in cross section, corresponding to n/D in the case of obtaining sliver by tearing off the tow, and accordingly the ratio of CV% to that of the tearing off case becomes the following. ##EQU1##
Generally, in the tearing off case, the drafting ratio D is much greater than 1 and the value of above equation is almost equal to 1. Therefore, even in the tearing off case, the uniformity of finess in the obtained spun yarn is at most the same as the uniformity in the random sliver. As is mentioned above, the conventional spinning methods are limited in uniformity of thickness in the obtained spun yarns.
On the other hand, many methods have been proposed to impart hand touchness like spun yarn to filament yarns as shown in Japanese Patent Publication No.36-6592, 40-19697 and 49-133639, in which methods of making nap on the surface of filament yarn are proposed. However, the spun like yarns obtained by these methods have nap on the surface of yarn and are apparently similar to spun yarn, but bulkiness and softness of them, and hand touchness of the surface of knitted and woven fabrics made of them are greatly inferior to those of spun yarn.
As an another method of manufacturing spun like yarn made of filament yarn, Japanese Patent Laying Open No.50-154550 has been proposed. According to this method, an unoriented polyester yarn is subjected to drafting and heat treatment at a specific condition to impart weak points in places to the filaments and tearing off the yarn to obtain spun-like yarn.
The end portions of fibers obtained by this method are not only on the surface of yarn but also inside the yarn and, therefore, the yarn obtained by this method is more similar to spun yarn than those obtained by above mentioned conventional methods. However, according to this method, weak points are quite randomly existed in each filament, so that the length of fibers obtained is quite irregular.
Well known methods for manufacturing the blended yarn are a method of blending plural staple fibers at a scutching process and a method of blending plural slivers at a drawing process or gilling process. However, the blended yarns obtained by these methods have problems in uniformity of finess and productivity.
Covered yarn is a yarn in which the function of core yarn component is to improve the mechanical properties of yarn (such as stretchability, bending strength) and the function of covering component is to improve the feeling properties of yarn (such as color, hand touchness). A typical known method for manufacturing covered yarn is a method in which a core yarn is fed onto a front roller of ring spinning frame, discharging it together with a drafted fleece from the front roller, twisting and taking up the yarn thus produced.
However this method is not efficient because of using a roving yarn by way of long spinning processes. Also, in this method, a fleece, which is produced by drafting the roving yarn, is limited in uniformity of thickness, so that uneven covering tends to appear to lower the quality of knitted and woven fabrics made of the covered yarn.
Heretobefore, it has been known that doubling yarn is directly manufactured by using pot spinning frame, in which a drafted roving yarn is fed into a cylindrical pot which is rotating at a high speed to twist, and when the volume of yarn in the pot reaches at a predetermined one, the yarn is discharged together with a separate yarn, and the doubling and twisting yarn thus produced is taking up as a cheese. This method is superior to the methods using ring spinning frame which require four steps of spinning, rewinding, doubling and twisting.
However, this method has several problems in practice.
First problem is that it is required to stop once the rotation of the pot at the time of yarn breakage. As is well known, while pot in the spinning process, the fiber bundle is pressed against the inner wall surface of the pot by the centrifugal force action, but when stopped the rotation of pat, the fiber bundle inside the pot get out of shape. Accordingly, when yarn breakage occurs in the pot, the whole yarn therein becomes yarn waste.
Second problem is that it is required to rewind the winded yarn in order to remove yarn shortcomings such as slub and nep. Especially it is an essential problem when staple fiber is used as a starting material for spun yarn. Moreover, in case of removing of yarn shortcomings from doubling yarn, the knot portion of yarn is enlarged.
As is mentioned above, the conventional pot spinning methods have various essential problems and, especially, it is very difficult to prevent lowering of efficiency and yield caused by occurrence of yarn breakage.